The present invention relates a method and device for resetting a subject""s circadian pacemaker or for treating other sleep or seasonal affective disorders.
Hendrickson, A. E., et al., Z. Zellforsch mikros Anat. 135:1 (1972).
Johnson, C. H., AN ATLAS OF PHASE RESPONSE CURVES OF CIRCADIAN AND CIRCATIDAL RHYTHMS, Vanderbilt Univ, 1990.
Moore, R. Y., et al., Brain Res. 42:201 (1972a).
Moore R. Y., et al., J. Comp. Neurol. 146:1 (1972b).
Stephan, F. K., et al., Proc. Nat. Acad. Sci. USA 69:1583 (1972).
Most animals have daily rhythms of behavior and physiology. These rhythms free-run with periodicities close to 24 hours (circadian) in the absence of environmental cues. Circadian rhythms are generated by endogenous pacemakers that can be entrained to the 24 hour day by external physical cues. Entrainment by external cues involves phase shifting the rhythm of the endogenous pacemaker to bring it into synchrony with normal geophysical cues. The most important entraining stimulus is exposure to light. For example, exposure to light in the early dark period (circadian time CT12-CT18) will phase delay the pacemaker, and exposure to light in the late dark period (CT18-CT24) will phase advance the pacemaker (Johnson).
The circadian clock is important in the regulation of many circadian rhythms, including regulation of pineal gland metabolism, and melatonin secretion. In mammals, the circadian pacemaker resides in a group of hypothalamic neurons, the suprachiasmatic nucleus (SCN) (Moore, 1972a; Stephan) that receives direct connection from retinal ganglion cells (Hendrickson; Moore, 1972b).
Most people have a circadian cycle of about 24 hours, with variations of up to one hour in either direction being common. Under normal light cycles, these cycles are maintained in synchrony with normal geophysical cues. However, when a person fails to receive normal light cues, particularly due to light deprivation as occurs in winter months at extreme latitudes, or in heavily overcast environments, the circadian clock can free-run out of synchrony with the environment, causing sleep disorders, depression, and other symptoms classed generally as seasonal affective disorder (SAD). A common treatment for SAD is to expose the subject to high-intensity visible light for periods of 2-3 hours in the early morning. This treatment is usually carried out with banks of fluorescent lights.
It would be desirable to provide a method and device for treating SAD without the need for special high-intensity lighting, and without the requirement for long exposure to high-intensity of light.
A person""s circadian cycle must also be reset when travelling between time zones. There are ways that readjusting to a new day/night light cycle can be accelerated, but in general, the process is one of slowly readjusting to the new time zone through a period of xe2x80x9cjet-lagxe2x80x9d.
It would be desirable to provide a method and device that would allow a traveller to systematically and relatively quickly adjust his or her circadian clock to a new time zone.
In invention includes, in one embodiment, a method of phase shifting the circadian pacemaker or treating seasonal affective disorder in a subject. The method includes exposing the subject""s eye region to a given-intensity light flash having a flash duration of between about 1-500 msec, at a periodicity of between about one flash per 5 to 60 secs, i.e., 1 to 20 times per minute, over a selected time period effective, were the subject exposed to a continuous light pulse of the same intensity for this period, to phase shift the circadian pacemaker or treat the seasonal affective disorder in the subject.
The flash duration is preferably between about 1-25 msec (milliseconds), more preferably between about 1-5 msec.
The period of exposure is typically between about 5-180 minutes, typically 15-150 minutes. The total exposure time may be in the range as low as 120-600 msec, for example, 2 msec flashes, 2 per minute, over a 30 minute period (120 msec), or 2 msec flashes, 5 per minutes, over a 60 minute period (600 msec).
For use in phase advancing the subject""s circadian pacemaker, and for treating SAD, the exposing is preferably carried out during the subject""s circadian time CT18 to CT24, preferably CT22 to CT24. For use in phase retarding the subject""s circadian pacemaker, the exposing is preferably carried out during the subject""s circadian time CT12 to CT18, preferably CT12 to CT14.
In another aspect, the invention includes a device for phase shifting the circadian pacemaker or treating seasonal affective disorder in a subject. The device includes a visible light emitter adapted to be supported at a position to provide a light exposure to the subject""s eyes, a control unit for activating the light emitter to emit a light flash of a given intensity having a flash duration of between about 1-500 msec, at a frequency of at least about one flash per minute, over a selected time period effective, were the subject exposed to a continuous light pulse of the same intensity for this period, to phase shift the circadian pacemaker or treat the seasonal affective disorder in the subject, and structure for connecting the light emitter and control unit to a power source.
In one general embodiment, the light emitter is a strobe light. In another, such as for use with a pair of eyeshades, the device is a photodiode or photodiode array. The control unit is preferably operable to activate a light flash duration between about 1-25 msec, more preferably, between about 1-5 msec.
The control unit may include a timer for activating light flashes over a selected treatment period of preferably between 5 and 180 minutes.
For use in phase advancing or phase retarding the subject""s circadian pacemaker, the control unit is designed to determine, from subject input about the extent and direction of circadian pacemaker phase change desired, the optimal treatment time. The unit may be designed to determine such optimal treatment time for each treatment at each of several successive days. It may also be operable to adjust light flash intensity and/or duration.
In a more specific aspect, the invention includes a portable eyeshade device for phase shifting the circadian pacemaker or treating seasonal affective disorder in a subject. The device includes an eyeshade mask adapted to worn by the subject, visible light emitters positioned within the mask to provide a light exposure to the subject""s eyes, when the mask is being worn, a control unit for activating the light emitters to emit a light flash of a given intensity having a flash duration of between about 1-500 msec, at a periodicity of at least about one flash per minute, over a selected time period effective, were the subject exposed to a continuous light pulse of the same intensity for this period, to phase shift the circadian pacemaker or treat the seasonal affective disorder in the subject, and structure for connecting the light emitters and control unit to a power source.
These and other objects and features of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.